Rendering out Alpha masks for compositing

I would like to see another way to create alpha masks not material ID’s, for elements in a scene for post processing/ compositing. I like the way Maxwell Render does it. I can create a render channel, similar to a render layer, but I can simply assign either objects or materials to the render channel to be rendered as alpha masks. The object can be a mixed material object as well. The masks can be opaque or an RGBA mask. It is so easy to use in Maxwell Render and it does not depend on the objects respective layer. Only the material it uses or the object itself. Render layers are a bit cumbersome when I need some quick masks for post processing.

maybe try compiling blender with this patch? it probably would suit the needs of what you are after –

Ho Jul 15 2016, Wooow!
Very good initiative! and with EXF format, fine!

When in the trunk, please doublebishop ?
Thanks for infos!

This looks like what I want especially with the compositor node that changes the Material Id’s to black and white mattes. I do not know how to compile Blender with a patch. I will look into how to do that, unless there is a simple way to describe the process to me?

I downloaded the Is this what I need? Have you tried Cryptomatte with Blender?

This is a tool that must get into Blender trunk.

You can use object ID instead of material ID. This works flawlessly for me. You will need to apply color correction usually though to get the mask to show up in your compositor (I use Natron and Nuke)